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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 192 |
| 4 | 812 |
| 5 | 3284 |
| 6 | 13700 |
| 7 | 54768 |
| 8 | 219160 |
| 9 | 877820 |
| 10 | 3511440 |
| 11 | 14050304 |
| 12 | 56246708 |
| 13 | 225125676 |
| 14 | 901087684 |
| 15 | 3606684324 |
[1,4,36,192,812,3284,13700,54768,219160,877820, 3511440,14050304,56246708,225125676,901087684, 3606684324] |